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Implementing the IRenderingExtension Interface

The rendering extension takes the results from a report definition that is combined with the actual data and renders the resulting data to a format that is useable. The transformation of the combined data and formatting is done by using a common language runtime (CLR) class that implements IRenderingExtension. This transforms the object model into an output format that is consumable by a viewer, printer, or other output target.

The IRenderingExtension has three methods that must be coded:

The following sections discuss these methods in more detail.

The Render method contains arguments that represent the following objects:

  • The report that you want to render. This object contains properties, data, and layout information for the report. The report is the root of the report object model tree.

  • The ServerParameters that contain the string dictionary object, with the parameters for the report server, if any.

  • The deviceInfo parameter that contain the device settings. For more information, see Passing Device Information Settings to Rendering Extensions.

  • The clientCapabilities parameter that contains a NameValueCollection dictionary object that has information about the client to which you are rendering.

  • The RenderProperties that contains information about the rendering result.

  • The createAndRegisterStream is a delegate function to be called to get a stream to render into.

deviceInfo Parameter

The deviceInfo parameter contains rendering parameters, not report parameters. These rendering parameters are passed to the rendering extension. The deviceInfo values are converted into a NameValueCollection object by the report server. Items in the deviceInfo parameter are treated as case-insensitive values. If the render request came as a result of URL access, the URL parameters in the form rc:key=value are converted to key/value pairs in the deviceInfo dictionary object. The browser detection code also provides the following items in the clientCapabilities dictionary: EcmaScriptVersion, JavaScript, MajorVersion, MinorVersion, Win32, Type, and AcceptLanguage. Any name/value pair in the deviceInfo parameter that is not understood by the rendering extension is ignored. The following code sample shows a sample GetRenderingResource method that retrieves icons:

public void GetRenderingResource (CreateStream createStreamCallback, NameValueCollection deviceInfo)
{
    string[] iconTagValues = deviceInfo.GetValues("Icon");
    if ((iconTagValues != null) && (iconTagValues.Length > 0) )
    {
        // Create a stream to output to.
        Stream outputStream = createStreamCallback(m_iconResourceName, "gif", null, "image/gif", false);
        // Get the GIF image for one of the buttons on the toolbar
        Image requiredImage = (Image) m_resourcemanager.GetObject(m_iconResourceName
        // Write the image to the output stream
        requiredImage.Save(outputStream, requiredImage.RawFormat);
    }
    return;
}

The RenderStream method renders a particular stream from the report. All streams are created during the initial Render call, but the streams are not returned to the client initially. This method is used for secondary streams, such as images in HTML rendering, or additional pages of a multi-page rendering extension, such as Image/EMF.

The GetRenderingResource method retrieves the information without executing an entire rendering of the report. There are times when the report requires information that does not require the report itself to be rendered. For example, if you need the icon associated with the rendering extension, use the deviceInfo parameter containing the single tag <Icon>. In these cases, you can use the GetRenderingResource method.

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